Growth in the semiconductor industry has been driven by advances in plasma processing. Due to the highly competitive nature of the semiconductor, device manufacturers may want to maximize yield and efficiently utilize the real estate available on a substrate. During plasma processing of the substrate, a plurality of parameters may need to be controlled to ensure high yield of devices being processed. A common cause of defective devices is the lack of uniformity during substrate processing. Factors that may affect uniformity are substrate edge effects. Another cause of defective devices may be due to polymeric by-products flaking off from the backside of one substrate onto another substrate during transport.
Current fabrication technologies are challenged by the demand for higher performance devices, the pressure to further reduce substrate feature sizes, as well as the implementation of newer optimized substrate materials. For example, it is becoming increasing difficult to maintain the uniformity or process results from the center to the edge of larger substrates (e.g., >300 mm). In general, for a given feature size, the number of devices on the substrate near the edge increases as the size of the substrate becomes larger. Likewise, for a given substrate size, the number of devices on the substrate near the edge increases as the feature size of the devices decreases. For example, often over 20% the total number of devices on a substrate are located near the perimeter the substrate.
FIG. 1 shows a simplified diagram of a capacitively-coupled plasma processing system with a single hot edge ring. In general, a source RF generated by source RF generator 112 is commonly used to generate the plasma as well as control the plasma density via capacitively coupling. Certain etch applications may require upper electrode to be grounded with respect to a lower electrode, which is RF powered. The RF power is at least one of 2 MHz, 27 MHz, and 60 MHz. Still other etch applications may require both the upper electrode and the lower electrode to be RF powered using similar RF frequencies.
Generally, an appropriate set of gases is flowed through an inlet in an upper electrode 102. The gases are subsequently ionized to form plasma 104, in order to process (e.g., etch or deposit) exposed areas of substrate 106, such as a semiconductor substrate or a glass pane, positioned with a hot edge ring (HER) 116 (e.g., Si, etc.) on an electrostatic chuck (ESC) 108, which also serves as a powered electrode.
Hot edge ring 116 generally performs many functions, including positioning substrate 106 on ESC 108 and shielding the underlying components not protected by the substrate itself from being damaged by the ions of the plasma. Hot edge ring 116, as shown in FIG. 1, is disposed under and around the edge of substrate 106. Hot edge ring 112 may further sit on coupling ring 114 (e.g., quartz, etc.), which is generally configured to provide a current path from chuck 108 to hot edge ring 116.
In the example of FIG. 1, insulator rings 118 and 120 are configured to provide insulation between ESC 108 and ground ring 122. Quartz cover 124 is disposed on top of ground ring 122. Material for coupling ring 114 may be quartz or appropriate material to optimize RF coupling from ESC 108 to HER 116. For example, quartz may be employed as coupling ring 114 to minimize RF coupling to HER 116. In another example, aluminum may be employed as coupling ring 114 to get increase RF coupling to HER 116.
Due to substrate edge effects, such as electric field, plasma temperature, and the loading effects from process chemistry, the process results near the substrate edge may differ from the remaining (center) area of the substrate during plasma processing. For example, the electric field around substrate 106 edge may change due to changes from RF coupling to HER 116. The equipotential lines of the plasma sheath may become disrupted, causing non-uniform ion angular distribution around the substrate edge.
Generally, it is desirable for the electric field to remain substantially constant over the entire surface of the substrate in order to maintain process uniformity and vertical etch profiles. During plasma processing, RF coupling balance between substrate 106 and HER 116 may be optimized by design to maintain process uniformity and vertical etch. For example, RF coupling to HER 116 may be optimized for maximum RF coupling to get uniform etching. However, the RF coupling balance to maintain process uniformity may come at a cost to beveled edge polymer deposition.
During the etch process, it may be common for polymer byproducts (e.g., fluorinated polymers, etc.) to form on the substrate backside and/or around the substrate edge. Fluorinated polymers generally are comprised of photo resist material previously exposed to an etch chemistry, or polymer byproducts deposited during a fluorocarbon etch process. In general, a fluorinated polymer is a substance with a chemical equation of CxHyFz, where x, z are integers greater than 0, and y is an integer greater than or equal to 0 (e.g., CF4, C2F6, CH2F2, C4F8, C5F8, etc.).
However, as successive polymer layers are deposited on the edge area as the result of several different etch processes, organic bonds that are normally strong and adhesive will eventually weaken and peel or flake off, often onto another substrate during transport. For example, substrates are commonly moved in sets between plasma processing systems via substantially clean containers, often called cassettes. As a higher positioned substrate is repositioned in the container, a portion of a polymer layer may fall on a lower substrate where dies are present, potentially affecting device yield.
FIG. 2 shows a simplified diagram of a substrate in which a set of edge polymers have been deposited on the planar backside is shown. As previously stated, during the etch process, it may be common for polymer by-products (edge polymers) to form on the substrate. In this example, the polymer by-products have been deposited on the planar backside, that is, the side of the substrate away from the plasma. For example, the polymer thickness may be about 250 nm at about 70° 202, 270 nm at about 45° 204, and about 120 nm at 0° 206. In general, the greater the thickness of the polymer, the higher the probability that a portion of the polymer may become dislodged and fall onto another substrate or the chuck, potentially affecting manufacturing yield.
For example, RF coupling to HER 116 may be optimized for minimal RF coupling to reduce polymer by-products deposition on beveled edge. However, the RF coupling balance to minimize beveled edge polymer deposition may come at a cost to maintain process uniformity at substrate edge.
Hence, aforementioned prior art methods require RF coupling balance between the hot edge ring and the substrate to trade-off between optimizing for edge uniformity or beveled edge polymer deposition. In addition, arcing between the wafer edge and hot edge ring may cause pitting on substrate edge and damage to the devices, thereby reducing yield.